Are there any conventions in mainstream surround-sound mixing (big Hollywood films) with regards to how low frequency bandwidth is allocated? In other words, is there any reason to NOT use the LFE channel(s) for bass frequencies and to send discrete low frequency information to the center or front channels...even to the surround/rear? My initial guess would be "no" due to the omnidirectional nature of those frequencies, but then again, you do see healthy-sized center and main channels in both professional and consumer cinema systems.

Also, are there any general guidelines that the mixing engineers follow with regard to the frequency range for the specific channels? Such as.."o.k., we general don't send anything below 75 Hz to the center channel.." etc.

I've noticed that the overwhelming majority of professional cinema systems are made by JBL, so I'm guessing the audio is mixed with those in mind?

And as I've gone ahead and asked 10 questions instead of just one ...I'll go ahead and ask one more.... are the blu ray releases the same surround mix as the theatrical releases?

Just curious..and would like to know because I'm about to drop some cash for a surround system.

The important thing to consider about very low frequencies is that they are likely to reproduce differently in different venues and will generally reproduce differently in different areas of a single venue. For instance, very low frequencies may sound very faint in some parts of a theater and yet be overpowering in others, such as near the back wall, due to the effects of the nodes and antinodes of standing waves produced in all rooms (except anechoic chambers). The issue is especially pronounced with sustained sounds. For this reason I very rarely send sustained low frequency sounds to the LFE. I prefer to send short pulses that have impact, but do not linger long enough to mask other sounds or become irritating if they are emphasized by a room mode, and conversely will not sound like something is missing if they are cancelled out. I also like to think of the LFE as an audio exclamation point to put special emphasis on a sound. If one overuses exclamation points, they lose their impact, so I believe they should be reserved for special occasions, rather than constant usage. That's just my personal opinion.

If you don't need to send low frequencies to the LFE to achieve the sound you are looking for, I wouldn't do it. It can be problematic when trying to make the mix translate properly for the LtRt print master, when the LFE must be bussed to the front speakers. The LFE speaker is calibrated 10dB louder than the mains and has extended low end in theatrical B chains, so simply bussing it to the front speakers will not result in a perfect match.

Surround speakers are usually smaller and less capable of reproducing low frequencies without distortion, so while you can send the full frequency spectrum to them, you could be pushing your luck with extremely dynamic low frequency sounds.

The final thing to consider is that in many theaters, the speakers least likely to be calibrated properly or replaced when they go bad are the surrounds and the subs. They are the weakest links in the B chain.

Hi my view is that you must make the screen channels work and use the LFE (and surrounds I guess) be the icing on the cake. Some systems will re-direct (bass management ) but all theaters are supposed to have full range screen channels.
I like many mixers have made the mistake of using the lfe channel as a glorified LF eq with varied results. Use divergence to spread the load over the screen channels if you are worried or struggling with band width and lick the lfe into life for that extra bit

Are the subs in a theater for LFE only, or are they also pushing main channel frequencies below 80hz (the THX crossover freq)?

I think you are asking whether the subs are used for bass management in movie theaters.

The LFE is not the same as bass management. The LFE is used as a special effect channel that can push low frequencies to extreme levels using special speaker design and increased gain. The sub can perform both functions, but bass management is not used in movie theaters as a rule. It is often used for home theaters, however.

Bass management is a way of extending the low end frequency response of main speakers with small woofers, generally 10" or less, in small room near and mid field conditions where the mains are incapable of reproducing frequencies below about 80Hz accurately. Bass management also helps to deal with small room standing waves by allowing a single sub speaker to be placed in an ideal position that helps minimize the excitation of modal frequencies in the 40Hz to 80Hz range that tend to stack up in small rooms.

These issues are less of a factor in large theaters unless they are poorly designed and lack proper acoustic treatment. Theatrical main speakers generally use multiple 15" woofers that are capable of reproducing very low frequencies accurately. Also, large rooms can be designed so that the problematic low frequency room modes are below the useful range and so can be eliminated using high pass filters without hurting the accuracy of the mix, so special placement of a single sub woofer is not necessary for dealing with low frequency room modes.

The important thing to consider about very low frequencies is that they are likely to reproduce differently in different venues and will generally reproduce differently in different areas of a single venue. For instance, very low frequencies may sound very faint in some parts of a theater and yet be overpowering in others, such as near the back wall, due to the effects of the nodes and antinodes of standing waves produced in all rooms (except anechoic chambers). The issue is especially pronounced with sustained sounds. For this reason I very rarely send sustained low frequency sounds to the LFE. I prefer to send short pulses that have impact, but do not linger long enough to mask other sounds or become irritating if they are emphasized by a room mode, and conversely will not sound like something is missing if they are cancelled out. I also like to think of the LFE as an audio exclamation point to put special emphasis on a sound. If one overuses exclamation points, they lose their impact, so I believe they should be reserved for special occasions, rather than constant usage. That's just my personal opinion.

If you don't need to send low frequencies to the LFE to achieve the sound you are looking for, I wouldn't do it. It can be problematic when trying to make the mix translate properly for the LtRt print master, when the LFE must be bussed to the front speakers. The LFE speaker is calibrated 10dB louder than the mains and has extended low end in theatrical B chains, so simply bussing it to the front speakers will not result in a perfect match.

Surround speakers are usually smaller and less capable of reproducing low frequencies without distortion, so while you can send the full frequency spectrum to them, you could be pushing your luck with extremely dynamic low frequency sounds.

The final thing to consider is that in many theaters, the speakers least likely to be calibrated properly or replaced when they go bad are the surrounds and the subs. They are the weakest links in the B chain.

Gary,

Thanks for the reply and the info.

So, given what you're saying, on your run-of-the-mill (if there is such a thing) big-budget hollywood film mixed in 5.1 or 7.1..as far as the surround mix on the final retail blu ray is concerned...it would be very likely to have discrete full-bandwidth signals (i.e. with intentional bass frequencies included) on the front/mains but very unlikely to have discrete full-bandwidth signals sent to the surrounds and/or rears?

In other words, the mixing engineers will generally assume the use of smaller, partial-range surround speakers in commercial theaters and in private home theaters and, thus, they will intentionally withhold or cut low frequency information from those channels in the final mix?

So, given what you're saying, on your run-of-the-mill (if there is such a thing) big-budget hollywood film mixed in 5.1 or 7.1..as far as the surround mix on the final retail blu ray is concerned...it would be very likely to have discrete full-bandwidth signals (i.e. with intentional bass frequencies included) on the front/mains but very unlikely to have discrete full-bandwidth signals sent to the surrounds and/or rears?

Reasonably full range in movie theaters, but not as robust as the mains.

Full frequency to the surrounds is fine in some circumstances. But if the bass frequencies of a sound are particularly dynamic, then I might reduce them, depending on how loud I needed to play the sound in the surrounds. You just have to be aware of what the surround speakers are capable of handling, with the caveat that in the real world the surrounds may be less capable than those on a high end dub stage.

A home theater setup that uses bass management for both the mains and the surrounds sends the frequencies below 80Hz to the subwoofer, so not an issue. If not using bass management, the surrounds may not be able to reproduce the lows, meaning you may not hear them or they may distort, depending on the system. That doesn't mean that the low frequencies won't be present in the signal, though.

The dolby cinema processors band limit the surrounds. Its a little hard to replicate with out a cp650/etc but the screen channels are full range. Dolby spec requires 105 (or is it 110db) with out distortion at the mix position, and so cinemas are supposed to be the same

I think you are asking whether the subs are used for bass management in movie theaters.

Not quite. I'm wondering if the mains in a theater can cleanly produce low frequencies found in musical content. ie. I have a part in a passage where the kick drum is meant to "shake the room" so-to-speak (not quite cannon fire level or anything, but it is a "musical effect" of sorts). Should I mix some of the kick to the LFE, or can the mains in a modern theater handle low-frequency content? Right now it's just a 4.0 mix meant for home theater, but may be screened in a real theater.

Not quite. I'm wondering if the mains in a theater can cleanly produce low frequencies found in musical content.

Yes. The mains are trully full range. It can handle most of the "normal" low frequencies. All the big orchestra score complete with percusion sections are reproducable just fine with only the mains. You can even add sub-harmonic enhanced tracks and to be reproduced just fine, minding you contained/controlled the dynamic off-course.

And I just want to stressed what Gary has explained, the LFE is intended just for that "Ooomph" effect and need to be used extremely wisely.

Speaking of music/score mix--most (99%) of the time it was mixed full range to 4.0 only (not using the center channel and LFE). As in stereo music mix, most of the time we need to pan any bass heavy instrument front and (phantom) center. But perhaps this is for other thread.

Yes. The mains are trully full range. It can handle most of the "normal" low frequencies. All the big orchestra score complete with percusion sections are reproducable just fine with only the mains. You can even add sub-harmonic enhanced tracks and to be reproduced just fine, minding you contained/controlled the dynamic off-course.

I see. Thanks. So do theaters typically have a separate sub dedicated for LFE?

Quote:

And I just want to stressed what Gary has explained, the LFE is intended just for that "Ooomph" effect and need to be used extremely wisely.

Yeah. I'd prefer not to mess with the LFE at all, but was wondering if the theater mains could handle the sub-bass frequencies (20-35hz) in a particular music passage without farting out...

Out of curiosity, I'd love to see an audio spec sheet of a typical theater (type/size of speaker, frequency response and crossover frequencies, etc). Anyone know have any links?

In your experience what is the norm? I would have thought the vast majority of home surround systems would have bm.

I think you are correct. I do not use bass management for the surrounds when pre dubbing feature films in my small mix room, only the front speakers, because doing so does not accurately reflect what I would hear on a large dub stage. However, when I am mixing TV and Cable projects, I do use BM for the surrounds.

Regarding 6string's question about the kick drum, I would suggest delivering it as a separate stem feeding the mains and allow the rerecording mixer to determine how to deal with it in the mix.